1. Field of the Invention
The present invention relates to a printer in which roll paper is pulled by the end thereof and supplied to a printing unit by advancement of a transportation roller, and the printer prints to the surface of the supplied roll paper, and relates more particularly to a pulling load-buffering device for buffering the load acting on the roll paper when the roll paper is thus pulled.
2. Description of Related Art
Printers which internally house roll paper, that is, a long length of recording medium in roll form, and which pull this paper by means of a transportation roller to print to the surface of the paper, are widely known. It is generally preferable to install a large diameter roll of paper in this type of printer to reduce the frequency of roll paper replacement. A problem with this is that as roll paper diameter increases, great tension acts on the pulled part of the paper as a result of the inertia tending to keep the roll paper stationary when it is pulled. This produces slippage between the transportation roller and paper, and can cause the paper to tear. A number of load-buffering devices for reducing the load on the roll paper have thus been proposed.
FIG. 11 shows an example of a conventional load-buffering device. As shown in the figure, a load-buffering device 1 is disposed between a location where the roll paper R is placed and a print unit 5. On one end of an arm 2 removably supported on a case so that it can pivot, the load-buffering device 1 has a roller 3 around which a part r of the pulled out roll paper is draped. A spring 4 biases the arm 2, in the counterclockwise direction in the figure, to resist a rotary movement of the arm 2 in the clockwise direction. Tension applied to the paper when the transportation roller 6 pulls the roll paper, causes the arm 2 to pivot in the clockwise direction as seen in the figure until a balance is reached between the force of the spring 4 resisting such pivotal movement and the force required to rotate the roll paper. This movement of the arm 2 causes the tension on the paper to increase gradually to the amount required to draw paper off the paper roll, in contrast to a sudden increase that would occur without the load-buffering device.
However, there are a number of problems with the above conventional load-buffering device as described below.
(1) When transport roller 6 starts pulling the paper, the direction in which the paper is pulled and the direction in which the arm 2 is moved are substantially opposite to each other. The relative distance between the transportation roller 6 and the roller 3, and between the roll part (point A in the figure) of the roll paper and the roller 3, changes according to the angle of rotation of the arm 2, resulting in excessive paper tension on one side of the roller 3 and slack in the paper on the other. As a result, smooth advancement of roll paper R is hindered.
(2) The load-buffering device 1 requires sufficient space inside the printer case to assure a sufficient range of arm 2 movement. This tends to make the printer size larger than otherwise necessary.
(3) The precision in positioning the load-buffering device to the roll paper and print unit is important in order to assure stable operation of the load-buffering device. However, this is difficult to assure in mass printer production because installing the above noted conventional load-buffering device is independent of roll paper installation. Installation is also difficult.
(4) Depending on the printer installation, it is desirable to change where the roll paper is placed relative to the printer case, or to change the orientation of the user-supplied roll paper, that is, which side of the unrolled paper faces a particular direction. It is difficult to flexibly modify the configuration or installation of a conventional load-buffering device to handle such changes.
(5) It is also common in this type of printer to use a near-end sensor for detecting when there is little paper left on the roll. When the load-buffering device is modified as noted in (4) above, however, the position of the near-end sensor must also be changed and adjusted.
An object of the present invention is to provide a buffering device that does not interfere with smooth roll paper transportation.
Another object of the present invention is to minimize the installation space requirement of the buffering device and thus enable further downsizing of the printer.
Another object of the present invention is to improve the precision in the installation of the buffering device to the roll paper position, thereby assuring stable operation of the buffering device in a mass produced printer.
Another object of the present invention is to provide a load-buffering unit that allows the installation position to be readily changed when, for example, the location where roll paper is installed to the printer case is changed or the orientation of the printing surface of user-supplied paper is changed.
Another object of the present invention is to provide a near-end sensor element on the load-buffering unit in accordance with one embodiment of the present invention, to thereby eliminate the need for near-end sensor adjustment when the position of the load-buffering unit is changed.
To achieve the above objects, a roll paper pulling load-buffering device is provided for use in a printer that prints on a surface of roll paper that is supplied to a print unit by rotation of a transportation roller that pulls from an end of the roll paper. In one aspect, the roll paper pulling load-buffering device has an arm that is rotatably disposed and rotatable within a specified angle about a shaft for roll paper rotation; a roller extending from the arm widthwise to the roll paper on the outside of the paper roll so that the pulled out part of the roll paper can be draped therearound; and an urging means for urging the arm in a direction opposite to a direction in which the arm is moved circularly by the intervening roller due to force occurring when the roll paper is transported by the transportation roller.
The major part of arm movement in a load-buffering device according to the present invention is contained within the area in which the roll paper is stored. The overall area occupied by the load-buffering device is therefore extremely small with respect to the printer. The path of roller movement is also an arc centering on the shaft on which the roll paper rotates. Paper tension on both sides of the roller supporting the paper pulled off the roll therefore does not vary greatly in conjunction with the angle to which the arm rotates, and paper can therefore be pulled smoothly off the roll.
The roll paper pulling load-buffering device of the invention may preferably have an arc shaped guide centering on the shaft for roll paper rotation. In this case the urging means is preferably an extension spring stretching and contracting along the guide.
The roll paper pulling load-buffering device in this case further preferably has a second extension spring for urging the arm in a direction opposite to the urging direction of the above-noted extension spring.
In another embodiment, the urging means of the roll paper pulling load-buffering device may preferably be formed from a torsion spring wound around the shaft for roll paper rotation.
Yet further, in a preferred embodiment, the shaft for roll paper rotation, the arm, the roller, and the urging means of this roll paper pulling load-buffering device are assembled as a unit that is removable from and installable to the printer frame.
The present invention also relates to a roll paper pulling load-buffering unit that is removably installable to a frame of a printer that prints to a surface of roll paper. The roll paper may be supplied to a print unit of the printer by rotation of a transportation roller pulling from an end of the roll paper. The roll paper pulling load-buffering unit has an arm that is rotatable within a specified angle about a shaft for roll paper rotation, a roller and an urging device. The roller extends from the arm widthwise of the roll of paper, and located above the outside periphery of the roll of paper. The roller comes in contact with a pulled out part of the roll paper that is draped therearound. The urging means urges the arm in a direction opposite to a direction in which the arm is moved circularly by the intervening roller due to force occurring when the roll paper is transported by the transportation roller.
The roll paper pulling load-buffering unit of one embodiment may further preferably have a near-end sensor element for making a detection when the amount of print medium remaining on the paper roll is less than or equal to a specified amount.
In this case, the near-end sensor element is preferably adjustably disposed to a position relative to the diameter of the paper roll. In this case the near-end sensor element is selectively installed to any of plural fixed positions, or is installed to an appropriate position within a specific range of movement.
In addition, the roll paper pulling load-buffering unit may preferably have an arc-shaped guide centering on the shaft for roll paper rotation. The urging means is a first extension spring having one end thereof fixed to the pulling load-buffering unit side, and the other end fixed to a member of the printer frame side, so that the spring extends and contracts along the guide.
Yet further, preferably, the roll paper pulling load-buffering unit in this embodiment may additionally have a second extension spring for urging the arm in a direction opposite the urging direction of the first extension spring. One end of the second extension spring is also fixed to the pulling load-buffering unit side, and the other end fixed to a member of the printer frame side.
The member on the printer frame side to which the above-noted other end of at least one of the two extension springs is mounted may be adjustable.
Yet further preferably, the above-noted guide of this roll paper pulling load-buffering unit has a protruding part that contacts the above-noted adjustable mounting member to limit circular movement of the arm.